Tipis in an Atsina camp, on the plains of Montana. Photographed by Edward S. Curtis (American, 1868 - 1952) in 1908. The Gros Ventre, also known as the A'ani, A'aninin, Haaninin, and Atsina, are a historically Algonquian-speaking Native American tribe located in north central Montana. Today the Gros Ventre people are enrolled in the Fort Belknap Indian Community of the Fort Belknap Reservation of Montana, a federally recognized tribe with 3,682 enrolled members, that also includes Assiniboine people or Nakoda people, the Gros Ventre's historical enemies.